In a typical image-guided surgical procedure, pre-operative scan data, e.g., CT or MRI scan data, of a patient region is obtained. This is done conventionally by immobilizing a patient during a scan with a CT or MRI imaging machine. The patient is then moved to a surgical setting for treatment of the target region. During the surgical procedure, the scan data is used to reconstruct hidden or subsurface images of the patient target region, to guide or assist the surgeon in the surgical procedure. For example, the scan data may be used to reconstruct a subsurface image of the target region as seen from the position and orientation of a surgical instrument being held by the surgeon.
It is important, of course, for the coordinates of the scan-data images being shown to the surgeon to closely match the coordinates of the actual target region. For this reason, it is important to calibrate the scan data with the actual position of the patient, keeping in mind that the scan data is obtained in one location, and the patient is moved to another location for the surgical procedure. Where the target region is a patient's head region, this coordinate matching may be done by placing fixed-position fiducials on the patient's head during the scanning procedure, and retaining the fiducials at the same head positions for the surgical operation. Coordinate matching can then be done by aligning the positions of the fiducials in both reference frames. This approach relies on the fact that the fiducials placed on rigid, non-deformable structure (e.g., skull) are retained in substantially the same position (patient coordinates) for both the scanning and surgical procedures.
For other surgical regions, e.g., the spine, it is virtually impossible to retain fiducials at fixed patient coordinates between the scanning and surgical operations. In this case, it is necessary to recalibrate the positions of the fiducials in the patient coordinate system every time the patient moves or is moved. Ideally, the surgeon would want to forego the use of fiducials altogether, since their placement involves additional inconvenience to the patient and surgeon.
It would therefore be useful to provide an improved system for registering pre-op scan data in a patient coordinate system during a surgical operation, to be able to use the scan data to accurately construct subsurface image data corresponding to the actual patient coordinate system.
Also during a surgical operation, a surgeon will often wish to check the exact placement of surgical cut, or placement of a tool or implant at the patient site. This can be done conventionally, by taking a fluoroscopic image of the patient region, and displaying the 2-D image to the surgeon. Unfortunately, the surgeon will be limited in the number or times and duration of fluoroscopic imaging, due to the need to limit the amount of x-ray exposure to both the patient and medical personnel.
It would therefore be desirable to provide a method and system of virtual fluoroscopy that allows a surgeon to view a patient region “fluoroscopically” from a number of different angles, and over extended periods of view, without actually exposing the patient and others in the surgical theatre to exposure to x-rays.
In particular, it is would be useful to construct virtual fluoroscopic images in real time, e.g., without significant computation time.